1. Field of the Invention
The present invention relates to an assembly of an optical fiber and an optical fiber holder.
2. Description of the Related Art
In an optical fiber device, light is emitted from a light emitting element, such as a light emitting diode, and is converged on an end surface of an optical fiber by means of a lens, thereby light coupling is achieved. Also, light is emitted from an end surface of an optical fiber, then transformed into collimated light by means of a lens and is incident on a light receiving element, such as a photo-diode, thereby light coupling is achieved. The optical fiber is held in an optical fiber holder. A lens and a light emitting element (a light receiving element) are mounted in a receptacle. An optical fiber holder is connected to a receptacle such that the lens comes into focus on the end surface of the optical fiber (for example, JP2002-90584A). “The end surface of an optical fiber”, used herein, refers to a light exiting surface or a light incident surface of an optical fiber, i.e., a surface at the end portion of an optical fiber that is orthogonal to the direction of the axis of the optical fiber.
FIG. 1 is a cross-sectional view showing an example of a conventional optical fiber holder. Optical fiber 2 is inserted through throughhole 7 of optical fiber holder 1 with its end surface 2b facing lens 5 that is supported by receptacle 3. Optical fiber 2 is adhered to optical fiber holder 1 by the following steps. First, optical fiber 2 is pre-processed (the optical fiber coating is removed and the optical fiber is cut) and pre-processed optical fiber 2 is inserted through throughhole 7 of optical fiber holder 1 such that its end portion 2a protrudes from surface 1b of optical fiber holder 1 that faces receptacle 3. Next, UV (ultraviolet-ray) cure resin 11 is injected into gap 9 that is formed between inserted optical fiber 2 and throughhole 7. UV cure resin 11 spreads in gap 9 due to the capillarity phenomenon and fills gap 9. Then, resin 11 is irradiated with ultraviolet rays so as to be cured, thereby optical fiber 2 is adhered to optical fiber holder 1.
The reason why end portion 2a of optical fiber 2 protrudes from surface 1b of optical fiber holder 1 is as follows. UV cure resin 11 instantaneously reaches end portion 2a of optical fiber 2 due to the capillarity phenomenon. If end surface 2b of optical fiber 2 aligns with surface 1b of optical fiber holder 1, the resin that reaches end portion 2a of optical fiber 2 will spread onto end surface 2b of optical fiber 2, preventing light from passing through end surface 2b. This may cause the performance of an optical fiber device to deteriorate. Removing the resin sticking to end surface 2b requires a cleaning process. A similar phenomenon occurs when end surface 2b of optical fiber 2 is positioned inside throughhole 7 of optical fiber holder 1. In this case, it is quite difficult to completely remove the resin sticking to end surface 2b. In contrast, when end surface 2b of optical fiber 2 protrudes from surface 1b of optical fiber holder 1 that faces receptacle 3, the resin, after reaching surface 1b of optical fiber holder 1 due to the capillarity phenomenon, not only spreads along optical fiber 2 but also spreads on surface 1b of optical fiber holder 1 because no capillarity works ahead of surface 1b. The resin that spreads widely in this manner is less likely to reach end portion 2a of optical fiber 2 and is less likely to stick to the end surface of the optical fiber.
However, when the end portion of an optical fiber protrudes from the surface of an optical fiber holder, the end surface of the optical fiber is easily subject to mechanical shocks from the outside, although the resin is less likely to stick to the end surface of the optical fiber.